NTSB Identification: CEN16LA310 14 CFR Part 91: General AviationAccident occurred Friday, August 05, 2016 in Indianola, IAProbable Cause Approval Date: 07/26/2017Aircraft: PIPER PA-11, registration: N4707MInjuries: 2 Fatal.NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.The commercial pilot was using a company airplane to accumulate flight time and experience. Two witnesses reported seeing the airplane climbing after takeoff and noted that the airplane was flying slowly and that it had a “hard time getting any lift.” The airplane finally started to climb; however, the wings started rocking and the airplane subsequently descended into terrain. The witness statements were consistent with the prestall motions of the airplane. The pilot and passenger were employed as company ground personnel. According to company policy, the pilot was not allowed to fly with passengers, and the passenger was only allowed to fly with a company flight instructor. The pilot was not a flight instructor. Examination of the airplane revealed no mechanical anomalies that would have precluded normal operation. A postaccident estimation of the airplane's weight and balance showed that the airplane exceeded its maximum gross weight at the time of the takeoff. It is likely that the pilot’s inadequate preflight planning led to the airplane being operated above its maximum gross weight and degraded its climb performance and led to an aerodynamic stall.The National Transportation Safety Board determines the probable cause(s) of this accident as follows:The pilot's inadequate preflight planning, which resulted in the airplane being operated above its maximum gross weight, degraded its climb performance, and led to an aerodynamic stall during the initial climb.On August 5, 2016, about 1113 central daylight time, a Piper PA-11; N4707M, impacted a field while maneuvering near Indianola, Iowa. The airplane was destroyed by impact forces. The commercial pilot and a student pilot rated passenger sustained fatal injuries. The airplane was registered to and operated by Agri-Flite Inc under 14 Code of Federal Regulations Part 91 for the personal flight that was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The flight originated from Laverty Field Airport, Indianola, Iowa at 1045.According to the president of Agri-Flight Inc, the pilot and the passenger were employed by Agri-Flite Inc as ground crew personnel and not as a pilots. The pilot was not a company flight instructor, was not allowed to fly with passengers, and was only allowed to fly with company flight instructors. The passenger was only allowed to fly with company flight instructors and not with any other pilots. The president said that ground personnel were allowed to fly company airplanes in order to accumulate flight time, but it was not a method in which ground personnel would transition from their ground personnel positions to pilot positions within the company. The president said there were no upcoming company pilot positions available for the pilot or passenger and that ground personnel are allowed to fly company airplane as a benefit.On the day of the accident, the president saw the pilot perform at least two stop and go's in N4707M. The president said that the passenger was sitting outside of the company office using his phone and later speculated that the passenger was communicating with the pilot. The president said the pilot landed N4707M, and the student pilot got on board without the airplane being shut down. According to the company security video, they both departed in the N4707M toward the west.According to local law enforcement, two witnesses stated that they saw the airplane takeoff toward the east, and it appeared to be moving "very sluggishly." The said that appeared as if there was something wrong with the airplane because it was it was having difficulty in attaining enough speed to takeoff and "more trouble" climbing after it lifted off the runway. The airplane flew to the east, then circled to the west, continued to be flying "very slowly," and "a hard time getting any lift." The airplane finally started to climb but then the left wing "dipped down" toward the ground. The airplane seemed to wobble back and forth three or four times, first the left wing followed by the right wing dipping down toward the ground. The airplane then "dropped out of the air."The pilot held a commercial pilot certificate with an airplane single-engine land rating. He held a second class medical certificate dated November 6, 2015. The medical certificate was issued without any limitations. According to the operator's accident report, the pilot had accumulated about 260 hours of total flight time of which about 2.5 hours was in the same make and model as the accident airplane.A Federal Aviation Administration (FAA) Principal Airworthiness Inspector from the Des Moines Flight Standards District Office stated that the wreckage was oriented facing east on a 090-degree heading The airplane's left wing rested flat on the ground. The right wing root was up off the ground slightly due to how the fuselage was twisted and laying on its left side. The post-crash fire consumed all fabric from the left and right wings and fuselage. Small pieces of fabric were still attached to parts of the fuselage frame tubing. Flight control continuity was confirmed. The Continental A-65-8, serial number 33822-5-8, engine magnetos were broken out of the back of the engine but were on the accessory case. The propeller was still bolted to the flange. The left blade was splintered several inches from the hub. The separated portion was located on the ground, under the engine. Approximately 30 percent of the right blade was missing. The instrument panel and all instruments were badly damaged by the fire. The only recognizable instrument was the turn and slip indicator. The positions of the throttle, carburetor heat, and fuel selector could not be determined due to the condition of the wreckage.The FAA final Forensic Toxicology Fatal Accident Report for the pilot stated: no carbon monoxide detected in blood, cyanide testing not performed, no ethanol detected in urine, and no listed drugs detected in urine.The president of Agri-Flite Inc.said that based on a pilot's weight of approximately 225 pounds and a passenger's weight of approximately 285 pounds, N4707M had a weight above the maximum certified weight of the airplane. The calculated takeoff weight of the airplane for the accident flight was about 1,338 lbs and the maximum certified weight was 1,220 lbs.